user organisation (insert organisation)the utilization of a combined or hybrid offshore structure to...
TRANSCRIPT
1
User Organisation (Insert Organisation)
Status: Final
Version: XX
Date: 31/Jan/2018 Infr
astr
uct
ure
Acc
ess
Rep
ort
s
User Project (Floating Offshore Wind Turbine with
Controllable Waterplane Area)
Project Acronym (FWOT - CWA)Click or tap here to enter text.
Project Reference Number (id 1098)
Infrastructure Accessed UCC_MaREI_Ocean Emulator
2
ABOUT MARINET
The MaRINET2 project is the second iteration of the successful EU funded MaRINET Infrastructures
Network, both of which are coordinated and managed by Irish research centre MaREI in University College
Cork and avail of the Lir National Ocean Test Facilities.
MaRINET2 is a €10.5 million project which includes 39 organisations representing some of the top
offshore renewable energy testing facilities in Europe and globally. The project depends on strong
international ties across Europe and draws on the expertise and participation of 13 countries. Over 80
experts from these distinguished centres across Europe will be descending on Dublin for the launch and
kick-off meeting on the 2nd of February.
The original MaRINET project has been described as a “model of success that demonstrates what the EU
can achieve in terms of collaboration and sharing knowledge transnationally”. Máire Geoghegan-Quinn,
European Commissioner for Research, Innovation and Science, November 2013
MARINET2 expands on the success of its predecessor with an even greater number and variety of testing
facilities across offshore wind, wave, tidal current, electrical and environmental/cross-cutting sectors. The
project not only aims to provide greater access to testing infrastructures across Europe, but also is driven
to improve the quality of testing internationally through standardisation of testing and staff exchange
programmes.
The MaRINET2 project will run in parallel to the MaREI, UCC coordinated EU marinerg-i project which aims
to develop a business plan to put this international network of infrastructures on the European Strategy
Forum for Research Infrastructures (ESFRI) roadmap.
The project will include at least 5 trans-national access calls where applicants can submit proposals for
testing in the online portal. Details of and links to the call submission system are available on the project
website www.marinet2.eu
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant
agreement number 731084.
3
Document Details
Grant Agreement Number 731084
Project Acronym MaRINET2
Title Floating Offshore Wind Turbine with Controllable Waterplane Area
Distribution Public
Document Reference MARINET-TA1-FWOT-CWA – id1098
User Group Leader, Lead Author
José Gaspar IST/CENTEC [email protected]
User Group Members, Contributing Authors
Mojtaba Kamarlouei IST/CENTEC Carlos Guedes Soares IST/CENTEC
Infrastructure Accessed UCC_MaREI - Deep Ocean Basin
Infrastructure Manager or Main Contact
Florent Thiebaut
Document Approval Record
Name Date
Prepared by José Gaspar 22/01/2018
Checked by
Checked by
Approved by
Document Changes Record
Revision Number
Date Sections Changed Reason for Change
Disclaimer The content of this publication reflects the views of the Authors and not necessarily those of the European Union. No warranty of any kind is made in regard to this material.
4
Table of Contents Table of Contents .......................................................................................................................... 4
1 Introduction & Background ...................................................................................................... 5
1.1 Introduction .................................................................................................................... 5
1.1.1 FOWT platform ......................................................................................................... 5
1.1.2 WEC devices ............................................................................................................. 6
1.1.3 New concept ............................................................................................................ 6
1.2 Development So Far ......................................................................................................... 7
1.2.1 Stage Gate Progress .................................................................................................. 9
1.2.2 Plan for This Access ................................................................................................ 11
2 Outline of Work Carried Out ................................................................................................... 11
2.1 Setup............................................................................................................................ 11
2.1.1 Model assembly ...................................................................................................... 11
2.1.2 Model installation in the basin .................................................................................. 12
2.1.3 Days 3 and 4 .......................................................................................................... 13
2.1.4 Days 5 and 6 .......................................................................................................... 14
2.1.5 Days 7 - 10 ............................................................................................................ 15
2.2 Test plan....................................................................................................................... 17
2.3 Results ......................................................................................................................... 18
2.3.1 Free Decay Tests .................................................................................................... 18
2.3.2 Stability Analysis ..................................................................................................... 19
2.3.3 Hydrodynamic Analysis ............................................................................................ 19
2.4 Conclusions ................................................................................................................... 22
3 Main Learning Outcomes ....................................................................................................... 23
3.1 Progress made .............................................................................................................. 23
3.1.1 For This User-Group or Technology ........................................................................... 23
3.1.2 For Marine Renewable Energy Industry ..................................................................... 23
3.2 Key Lessons Learned ...................................................................................................... 23
4 Further Information .............................................................................................................. 24
4.1 Scientific Publications ..................................................................................................... 24
4.2 Website & Social Media .................................................................................................. 24
5 References ........................................................................................................................... 25
6 Appendices .......................................................................................................................... 26
6.1 Stage Development Summary Table ................................................................................ 26
5
1 Introduction & Background
1.1 Introduction
The utilization of a combined or hybrid offshore structure to support Wind Turbines (WT) and Wave Energy
Converters (WEC) brings important economic synergies and advantages on the exploration of offshore
renewable energy [1], such as an increment on the energy yield per unit area of ocean, reduction of
exploration costs by using the same electric grid infrastructure, logistic supply chain, operation and
maintenance (O&M) services and structure foundation. On the other hand, the WECs may be located on
the perimeter of the Offshore Wind Turbines (OWTs) in order to reduce the wave loads and open more
windows for O&M operations, and be used to smooth the power output, since waves are less variable and
more predictable than wind [1].
However, the wind and wave technologies are in different development phases, being the first a more
mature, proven and standardized technology, and so, a hybrid concept should be developed, optimized
and standardized from existent WT structure concepts and technologies. The hybrid offshore structures
may be bottom-fixed or floating (FOWT) type. The first are exclusively used for water depths until 50 m
while the second ones above 100 m [1].
1.1.1 FOWT platform
The demand on renewable energy has increased significantly in the recent years and the trend is toward
larger wind farms located in deeper water at great distances from the shore [2, 3] in order to benefit from
stronger and favourable winds. Meanwhile, FOWTs with power rates of 5 MW (and more in the future)
are becoming an economic viable and feasible solution over the fixed structures [2]. However, the FOWT
platform must have enough buoyancy to support the turbine and its own weight, rotational stability to
avoid capsizing and good response motions to the incoming waves in order to avoid larger dynamic loads
and compromising the turbine performance [2]. Several concepts have been proposed to solve these
design issues and can be classified in one of three categories, spar, tension leg platform (TLP) and semi
– submersible/hybrid structures [3]. These concepts present different advantages and disadvantages,
which together with the site characteristics, determine the selection of the appropriate one [4, 5].
This research work is dedicated to semi – submersible FOWT platform concept. The main advantage of
this concept is the complete construction of the platform in a dry deck at the shipyard and further
transportation to the exploration site with less expensive offshore vessels (e.g. simple tug vessels) and its
connection to pre – laid moorings. So, in comparison to other concepts, this approach reduces the risks
of offshore operations, mainly at harsh sea state conditions, and increases the available period of time for
platform offshore installation [5]. However, only a limited number of shipyards are available to build up
these platforms, which may lead to increased transportation and installation costs when located far from
the selected site. According to [5], the minimum width of a 20 m total draft trifloat platform with a
geometry similar to the DeepCWind is 67.30, 77.54 and 86.45 m, for 5, 7.5 and 10 MW rated power
turbines, respectively. On the other hand, as presented in the same research work [5], the available dry
docks in Europe have widths of 75 (one in Portugal), 85 (two in France and in Finland), 88.2 (one in
Germany), 90 (three in Denmark, France and Netherlands), 93 (one in Ireland), 100 (one in Spain) and
120 m (one in Great Britain).
Thus, for example, the construction of FOWT platforms in Portugal is limited to 5 MW turbines, and so,
bigger platforms must be manufactured far from Portuguese exploration sites, which substantially
increases the transportation costs even for platforms manufactured in Spain (Cadiz). On the other hand,
it is clear that building 10 MW FOWTs already push the available shipyards to their limits, with the
exception of the ones in Spain and Great Britain, which means that in the future will be even harder to
build up 15 and 20 MW FOWTs, as this is becoming the trend as presented in [6].
The fees of these larger dry docks are significantly higher than the smaller ones, and so, the platform size
should be optimized in order to reduce it, however without affecting its stability. There are also other more
6
cost effective solutions, such as the adaptation of disused shipyards or the construction of new ones, and
the creation of new assembly methods of semi-submersible platforms [5].
1.1.2 WEC devices
Some research studies have been made in order to combine a semi-submersible FOWT platform, such as
the WindFloat one, with point absorber WECs and Oscillating Wave Surge Converter (OWSC) [7]. This
WindFloat platform is made of three main columns however without a central one, as in the DeepCWind
case. The turbine is attached in one of the columns located at the extreme of the platform in order to
reduce the stresses on the connections made between all columns and to benefit from higher restoring
moments due to the increased arm that separates it to the other two columns [5]. The point absorber is
included between these three columns while in another concept, each column has inside one OWSC. These
research studies have shown that the WECs hardly affects the motions of the WindFloat platform, and so,
not affecting the system’s power production and integrity [7].
The WECs have been also proposed as motion suppression devices of the FOWT platforms in order to
increase the turbine aerodynamic performance [8], which in contrast to passive damping devices, such as
Anti-Roll Tanks (ARTs), Open-Bottom Tanks (OBTs), Tuned Mass Dampers (TMDs), Fins, Bilge Keels and
Heave Bottom Plates (HBP) [9], converts the suppressed energy into electrical power rather than discard
it. However, it was concluded that a trade-off must be made between the maximum platform motion
reduction and the maximum wave energy extracted from the WEC, because the first is achieved by shifting
the WEC to a lower natural frequency than the FOWT one, while the second is achieved by matching the
WEC and FOWT natural frequencies [8]. However, the geometry of these WECs are not specified.
Some numerical studies made on different arrangements of WECs [10, 11] have shown advantages in
using WECs arranged in circular arrays. The circle-segment array of WECs presents much less variance on
power production when compared to the rectangular ones, roughly three times lower on average [10].
The circular array (e.g. six WECs arranged in a hexagonal layout) are less sensitive to changes on the
device positioning, wave direction and frequency, and may offer a more predictable power at a variable
wave climate [11]. Moreover, closely-spaced arrays may offer more cost effective designs despite the loss
in hydrodynamic performance due to negative array interactions, because are not so detrimental to the
extraction of wave energy and, on the other hand, may contribute to important savings in infrastructure
materials, such as steel [11, 12].
More studies were developed on the same research issue however dedicated to point floater WECs made
of different shapes [12-15]. The simulations have shown that a cone-cylinder floater is a better wave
absorber than the hemisphere-cylinder and hemisphere floaters, because it has better hydrodynamic
properties and coefficients [12], despite not having a significant gain in average power when compared
to the other floater shapes. The utilization of these cone shaped floaters in circular arrays was also studied
for a layout of 12 WECs with radii of 15, 18 and 24 m, and it was found a better total extracted power for
the larger radius, despite of the increasing costs in the construction and maintenance of a bigger structure
[12]. The absorbed power is uniformly distributed in the circular arrangement while it is unevenly
distributed in the linear and grid type arrays, where the front floaters extract more power than the rear
ones [13], and thus, the circular array provides a better power quality (smoothness). It was as well found
a uniformity in the Power Take-Off (PTO) control parameters across all floaters in a circular array, while
they change substantially in linear and grid type ones [13, 14]. Thus, the circular array is easier to control.
1.1.3 New concept
The development of semi-submersible FOWT platforms with increasing dimensions, in order to
accommodate higher power wind turbines, is strongly associated with the available shipyards, which are
scarce and almost tight for the construction of 7.5 and 10 MW FOWT. So, the solution may be the
adaptation of existing infrastructures or the construction of new ones to accommodate these FOWTs,
however an economic analysis should be made to evaluate the costs (and fees) involved. On the other
hand, these additional costs may be minimized by new concepts that are disruptive or incremental
modifications of the existent platform architectures. This research work proposes one of these concepts
7
(Gaspar et al. [15]), as presented in Figure 1, with 12 cone-cylinder shape point WECs attached to a
floating platform made of one central column and six external columns. These floaters may be extracted
from the water to protect them from a storm or just for maintenance. However, they may be as well
installed in this resting position at the shipyard in order to avoid undesired contacts with the dock walls
and released when the platform leaves the dock. Then the floaters can be, by fixing or controlling their
positions, used to decrease the platform’s draft in order to overcome the harbor shallow waters until the
open sea is reached.
Figure 1. Conceptual drawing of a hybrid offshore structure. The floaters are in their operation mode, with
exception of one, which was extracted from the water for maintenance (right bottom view). (Adapted
from Gaspar et al. [15]).
The main functionality of these WECs is to provide extra hydrodynamic stability to the platform in order
to improve the aerodynamic performance of the wind turbine. This is performed by damping the floater
arm movements with oil-hydraulic PTOs (only cylinders are presented in Figure 1) and controlling the draft
of each WEC in order to generate a total hydrodynamic restoring moment opposed to the turbine inclining
moment. So, this approach may be faster to perform than the one that exclusively relies on the uneven
distribution of water ballast across the platform exterior columns, in particular for fast and constant
changes on the wind directions and speeds. This control approach may also benefit from using cone
shaped floaters instead of the hemisphere-cylinder ones, because they provide a larger range of floater
water plane areas. Moreover, this active stability control system is intended to be self-sustainable, because
it will operate with the energy extracted from the waves.
These WECs may be as well compensate the loss in hydrodynamic stability of a platform designed with
dimensions below the ones required for the same turbine rated power, when the dry dock width don’t
allow it. On the other hand, the WECs circular arrangement may provide all the benefits related to the
production of power from wave energy and already identified in the state-of-the-art literature. It is also
important to mention that this arrangement will be installed in a structure designed for a FOWT and so
benefiting economically from this synergy.
This design was developed from existing FOWT architectures and it will evolve as more numerical and
experimental simulations are performed and lessons are learnt. This paper presents the preliminary results
of this research work.
1.2 Development So Far
The concept, as presented in Figure 1, was designed according to guidelines presented in [2, 5] while a
simplified physical model was designed and built with a 1:27 geometric scale, as presented in Figure 2.
8
The model central column has a diameter of 160 mm and height of 945 mm, while the lateral columns a
diameter of 110 mm and height of 830 mm and the upper lateral columns a diameter of 50 mm and height
of 250 mm. The 12 connecting pontoons (6 on top and more 6 at the bottom) have a diameter of 50 mm
and length of 300 mm and the WECs diameter is 185 mm. The model waterline is 805 mm.
The model with no ballast at all weights 31.3 kg, but the displacement at operational draft is about 69.8
kg in fresh water. Thus, it was necessary to fill the ballast tanks with water (18.0 kg distributed between
the lateral columns plus 2.0 kg in the central column) and add 18.5 kg of lead in the bottom of the platform
so to achieve the desired draft and displacement, also lowering the Centre of Gravity (CG).
Figure 2. 1:27 scale model without (left view) and with WECs (right view).
The model was constructed in Portugal by the research team. Several materials were used during the construction, especially PVC (main material of the hull) and steel (upper frame, heave plates, most connections, etc.). A key element for the bottom connection between the central column and the lateral columns was modelled on SolidWorks® and 3D-printed in PLA. In order to avoid leakages and underwater openings, the compartments containing elements for connection were filled with foam, but all the vertical columns have hollow compartments that are easier to fill with ballast water from above the waterline in order to enhance stability and achieve the desired draft. A mast with dumbbells was inserted on top so the heeling moment caused by the weight of the wind turbine is fairly represented, even though the thrust force applied on the turbine could not be represented. The hexagonal frame on top is able to accommodate connections for 12 WECs via steel arms.
The physical model was constructed in separated parts in a way that it was possible to disassemble and reassemble it fast and with little effort. The fully assembled model becomes rigid due to screw connections between closed or dry surfaces and special connections between the columns made with clamps, wires and turnbuckles in truss-like configuration.
A numerical model was as well created with GeniE® (Figure 3) and was analysed with HydroD® as regards to seakeeping and stability (this software is integrated in SESAM interface, DNV-GL). However, only the hull was modelled in a first instance. Indeed, the system with 12 WECs around possess several degrees of freedom, it depends on PTOs’ modelling and non-linear effects of great importance acting on the floaters mainly due to wave-body interactions. It is therefore very important to calibrate the numerical model of the hull in order to better model numerically the whole assembly in a second instance, whereas viscous damping on small elements, heave plates’ influences, non-linear dynamics, etc. may all have their
9
contributions on the hull’s performance itself and this must be known before the whole assembly is systematically study.
Figure 3. 1:27 scale numerical model (left view) and wet surface mesh (right view).
Since the physical model was constructed from the beginning by the team, all data regarding mass
proprieties of the model were known a-priori. So the data was included in the numerical modelling, which
allowed the final model to have a finely calibrated 6x6 inertia (mass) matrix.
While a full model was made to calibrate the mass matrix and to be used in the stability analyses (Figure
3, left view), the remaining characteristics depend on the wetted surfaces and elements, so a second
model considering only the submerged hull and its wetted surfaces was made for the seakeeping analyses
for the final mesh (Figure 3, right view).
It is also important to highlight a few limitations brought by the numerical procedure. The linear
seakeeping code is based on the assumption of small motions of the platform in comparison to the wave
amplitudes; and only linear waves are considered. Thus, with increasing wave amplitude, the
correspondence between numerical and experimental deteriorates. Besides, only first-order effects were
considered so far, so the near-trapping modes and other second-order effects were fully neglected.
1.2.1 Stage Gate Progress
As presented in the previous sections, the research work was dedicated to an understanding of the main
basic principles (e.g. FOWT restoring moment and stability) underlying the design problem (e.g. turbine
performance and safe operation, shipyard dimensional limitations) through a review of the research
literature (Sections 1.1.1 and 1.1.2). It then continued on the formulation of a concept to solve the design
problem (Section 1.1.3) and a preliminary analytical analysis of the concept (Section 1.2) was performed
in order to support the conjecture. So, this research can be classified as being located at the Technological
Readiness Level (TRL) 2 (See 6.1).
Thus, the objective of next research stage is to achieve TRL 3 by performing experiments in a 3D basin in
order to validate the numerical model, investigating the PTO damping effects on the platform motions in
real generic sea states and the determination of the PTO absorbed power and platform natural periods.
The platform optimization is investigated by comparing the platform hydrodynamic behaviour in two
different scenarios, without and with point floater WECs. The second scenario is then analysed in more
detail by decomposing it into three more cases, infinite, finite and no PTO damping. The prototype scale
10
was selected to be located next to the bottom limit of the recommend interval of 1:25 – 100 (Section 6.1)
in order to have more accurate results.
The target measurements are the platform motion response amplitude operators (RAOs), natural periods,
damping ratios, mooring forces and PTO damping coefficients. The measurements are also used to fine
tune the numerical model (e.g. mass and inertia matrices). Regular and irregular waves are generated,
and the later scaled down from a 20-minute scale. Storm weather is simulated as well.
Previously completed:
Planned for this project:
STAGE GATE CRITERIA Status
Stage 1 – Concept Validation
Linear monochromatic waves to validate or calibrate numerical models of the system (25 – 100 waves).
Finite monochromatic waves to include higher order effects (25 –100 waves).
Hull(s) sea worthiness in real seas (scaled duration at 3 hours)
Restricted degrees of freedom (DofF) if required by the early mathematical models
Provide the empirical hydrodynamic co-efficient associated with the device (for mathematical modelling tuning).
Investigate physical process governing device response. May not be well defined theoretically or numerically solvable
Real seaway productivity (scaled duration at 20-30 minutes)
Initially 2-D (flume) test programme
Short crested seas need only be run at this early stage if the devices anticipated performance would be significantly affected by them
Evidence of the device seaworthiness
Initial indication of the full system load regimes
Stage 2 – Design Validation
Accurately simulated PTO characteristics
Performance in real seaways (long and short crested)
Survival loading and extreme motion behaviour.
Active damping control (may be deferred to Stage 3)
Device design changes and modifications
Mooring arrangements and effects on motion
Data for proposed PTO design and bench testing (Stage 3)
Engineering Design (Prototype), feasibility and costing
Site Review for Stage 3 and Stage 4 deployments
Over topping rates
Stage 3 – Sub-Systems Validation
To investigate physical properties not well scaled & validate performance figures
To employ a realistic/actual PTO and generating system & develop control strategies
To qualify environmental factors (i.e. the device on the environment and vice versa) e.g. marine growth, corrosion, windage and current drag
To validate electrical supply quality and power electronic requirements.
To quantify survival conditions, mooring behaviour and hull seaworthiness
Manufacturing, deployment, recovery and O&M (component reliability)
Project planning and management, including licensing, certification, insurance etc.
Stage 4 – Solo Device Validation
Hull seaworthiness and survival strategies
Mooring and cable connection issues, including failure modes
PTO performance and reliability
Component and assembly longevity
11
STAGE GATE CRITERIA Status
Electricity supply quality (absorbed/pneumatic power-converted/electrical power)
Application in local wave climate conditions
Project management, manufacturing, deployment, recovery, etc
Service, maintenance and operational experience [O&M]
Accepted EIA
Stage 5 – Multi-Device Demonstration
Economic Feasibility/Profitability
Multiple units performance
Device array interactions
Power supply interaction & quality
Environmental impact issues
Full technical and economic due diligence
Compliance of all operations with existing legal requirements
1.2.2 Plan for This Access
The access plan was presented and discussed with the infrastructure manager in order to guarantee the
accomplishment of the stage gate criteria. It was decided to use the Ocean Emulator basin, since it
provided the visiting team an easy access to the model to perform setup and non-planned activities, and
decay and inclination testing. The regular and irregular sea state requirements could be satisfied by the
basin and the mooring layout was defined with the manager according to what was available at the facility,
and so, three mooring lines were used, each one with a load cell. The wave measurement system was
performed with 6 wave probes and the model 6DoF motion was tracked with the Qualisys motion camera
system. The infrastructure manager was asked to provide access to the facility workshop in order to
perform unplanned modifications in the model parts, which were kindly granted under supervision. The
test schedule was planned for a 10-day visit and with the following tasks:
Basin setup and sensors calibration (1 day)
Wave calibration and model setup (1 day)
Model without WECs (2.5 days) testing:
o Decay and inclination tests (0.5 day)
o Regular wave tests (1 day)
o Irregular wave tests (1 day)
Addition of WECs on the model (0.5 day)
Model with WECs (5 days)
o Scenario (2 days) – infinite damping
o Scenario 2 (2 days) – damping
o Scenario 3 (1 day) – no damping.
Model removal and packaging.
2 Outline of Work Carried Out
2.1 Setup
2.1.1 Model assembly
The model parts were unpacked and assembled at the laboratory facility in the first visit day (11th of Dec.
2018). Some parts were damaged during transportation, however they were successfully repaired with a
special PVC glue given by the lab staff. Then, the model was fully assembled (Figure 4) by the end of the
day and rested for 15 hours in order to give time for a perfect cure of the glue and silicon. Meanwhile, the
supervisor presented the site (Figure 5), in the ocean basin, where the model and wave sensors would be
located. Then, the model scale, regular and irregular sea state conditions were discussed with the
supervisor in order to prepare the sensors calibration phase.
12
Figure 4. Experimental model. The model structural strength is achieved with tensioned cables, which can
be released for a faster and easier model disassembly.
Figure 5. Ocean Basin Emulator.
2.1.2 Model installation in the basin
The model was marked with its water line, lifted with a crane and moved into a separate zone in the basin,
next to the moving platform. Then, it was slowly delivered to the team researchers, already prepared in
the site. The model was unstable, even after filling it with ballast water, and was moved to the basin
platform, which was raised in order to support the model and to add it 16.2 kg of lead weights, which
corresponds to the volume that has been filled with foam at the bottom of the model structure (Figure 6).
Then the model was lowered and some heeling and inclination tests have been made and the model
hydrodynamic response was stable. The structure was then moved to a low depth site of the basin where
it was moored for a 15-hour leakage test.
13
Figure 6. Top and middle views showing the lead weights (white coloured blocks) added to the model
bottom. The ballast water was filled in each column through small pipes (top view) and the model was
moored to the access ladder for a 15-hour leak test (bottom view).
2.1.3 Days 3 and 4
Some leakages were detected in the repaired parts, however it was easy to repair them with extra glue
and silicon. Meanwhile, the floaters and arms have been assembled outside the basin and more model
ballast and stability calculations were performed during the curing phase. Then preliminary inclination
tests were made on the model, when no leakages were verified, in order to calibrate the six degrees of
freedom video tracking system (Figure 7). The video camera output data is highly dependent on the
distance of the tracking point to the model centre of gravity (CG), as the reference point, especially in the
heave and pitch motions, so important for this test plan. So the exact location of this CG was determined
14
and updated for different model configurations, made of different masses and water ballasts, with accurate
hydrostatic analysis.
Figure 7. Top view - camera and tag balls for 6DoF motion tracking. Bottom view – basin control and data
acquisition room.
The inclination tests were performed by placing a 200g weight in one of the model columns and measuring
the heel angle. This test was repeated for all model columns and for 86 cm and 90 cm drafts.
2.1.4 Days 5 and 6
Preliminary free decay tests were performed in order to determine the model Eigen period in heave, pitch
and roll motions (Figure 8). This test was repeated 3 times for accuracy. Then, the model was moored to
the basin platform with three catenary mooring lines selected according to the weight per meter, length
and laying distance requirements. Three load cells were properly calibrated and then attached to the
mooring lines for tension measurement (Figure 9).
15
Figure 8. Free decay and inclination testing.
Figure 9. Mooring lines in the Bow (top view) and stern (bottom view) sides.
The preliminary tests with regular waves were performed for 3 wave heights and 18 different periods
each in order to build up a smooth curve of Response Amplitude Operators (RAOs).
2.1.5 Days 7 - 10
The full tests were performed for 4 model configurations: 1. Model without point floater WECs, 2. Model
with point floater WECs – infinite damping, 3. Model with point floater WECs – finite damping, and 4.
Model with point floater WECs – no damping. The tests were performed in the following sequence: stability
check (just for configuration 1), inclination, regular and irregular wave testing. The details of each test
16
phase are presented in section 2.2. The model configuration 1 was tested in the 7th access day, the WECs
were installed in the model in the 8th day (Figures 10 and 11) and the last access dates were dedicated to
the testing of the last three model configurations.
Figure 10 – Model with point floater WECs. Top view – CG regulation with the addition of ballast water in
the outer columns. The central column could be filled with water ballast. Bottom view – model inclination
tests performed with WEC finite damping (rotational dampers).
Figure 11 – Model with point floater WECs. Simulation in irregular sea state conditions.
17
2.2 Test plan
The test plan was designed to add complexity to the experiment in a smoother way, as it was performed
across all the testing phases. This approach gave time and space for researchers to acquire skills and
experience, and to make last minute adaptations in the model, instrumentation and testing plan when
required. The 4-model configurations were tested, as presented in Table 2.1 (1. – 4.), and a last calibration
phase (5.) took place at the end of the experiment in order to move the wave sensors to the site where
the model was located for a correction of the readings.
Test Description
1. Model without point floater WECs
1.1 Stability check
1.1.1 200g of weight is added to the central column (185mm freeboard from deck)
1.1.2 200g of weight is moved between all six outer columns (…)
1.1.3 200g of weight is added to the central column (140mm freeboard from deck)
1.1.4 200g of eight is moved between all six outer columns (…)
1.2 Inclination test
1.2.1 Still water with no ballast
1.2.2 Free heave, roll and pitch oscillations
1.3 Inclination test with moorings (1.1m water depth)
1.3.1 Still water
1.3.2 Free heave, roll, pitch and yaw oscillations
1.4 Regular wave test
1.4.1 Amplitude(A)=0.01m, increasing time periods (Ti=0.6s,Tf=1.8s,ΔT=+0.2s), 64s runs
1.4.2 A=0.01m, increasing time periods (Ti=2s,Tf=3.4s,ΔT=+0.2s), changed to 128s runs
1.4.3 A=0.01m, increasing time periods (Ti=3.5s,Tf=3.8s,ΔT=+0.1s)
1.4.4 A=0.01m, time period of 4s
1.4.5 A=0.02m, decreasing time periods (Ti=4s,Tf=0.6s, ΔT=-0.2s)
1.4.6 A=0.04m, decreasing time periods (Ti=3s,Tf=1s, ΔT=-0.2s)
1.5 Irregular wave test
Pierson-Moskowitz (PM) spectrum, increasing peak periods Tp=1.05, 1.15, 1.27, 1.39, 1.49, 1.6, 1.7, 1.75 and 1.89s.
2 Model with point floater WECs – infinite damping
2.1 Inclination test with moorings (1.1m water depth)
2.1.1 Still water
2.1.2 Heave, roll, pitch, yaw, surge and sway free oscillations.
2.1.3 Metacentric height on central column with 1079g lead weight
2.1.4 Metacentric height on column ?? with 1079g lead weight
2.2 Regular wave test
2.2.1 A=0.01m, decreasing time periods (Ti=3s,Tf=0.6s, ΔT=-0.2s), 94s runs / 3008 samples
2.2.2 A=0.02m, time period of 1.4s, 94s runs / 3008 samples
2.2.3 A=0.04m, time period of 1.4s, 94s runs / 3008 samples
2.3 Irregular wave test
PM spectrum, increasing peak periods Tp=1.05, 1.15, 1.27, 1.39, 1.49, 1.6, 1.7, 1.75 and 1.89s.
3 Model with point floater WECs – finite damping
3.1 Inclination test
3.1.1 Still water (1m water depth)
3.1.2 Still water (1.1m water depth)
3.1.3 Heave free oscillation.
3.1.4 Addition of water ballast and start of new inclination tests
3.1.5 Still water
3.1.6 Heave, ?, roll and pitch free oscillations.
3.2 Regular wave test
3.2.1 A=0.01m, decreasing time periods (Ti=3s,Tf=0.6s, ΔT=-0.2s), 94s runs / 3008 samples
18
3.2.2 A=0.02m, time period of 1.4s, 94s runs / 3008 samples
3.2.3 A=0.04m, time period of 1.4s, 94s runs / 3008 samples
3.3 Irregular wave test
3.3.1 PM spectrum, increasing peak periods Tp= 1.15, 1.27, 1.39, 1.49, 1.6 and 1.7s.
4 Model with point floater WECs – without damping
4.1 Inclination test
4.1.1 Still water
4.1.2 Heave, roll, pitch, yaw, surge and sway free oscillations.
4.2 Regular wave test
4.2.1 A=0.01m, decreasing time periods (Ti=3s,Tf=0.6s, ΔT=-0.2s)
4.2.2 A=0.02m, time period of 1.4s
4.2.3 A=0.04m, time period of 1.4s
4.3 Irregular wave test
PM spectrum, increasing peak periods Tp= 1.15, 1.27, 1.39, 1.49, 1.6 and 1.7s.
5 Wave probes calibration
5.1 Regular waves
5.1.1 A=0.01m, increasing time periods (Ti=0.6s,Tf=3.4s, ΔT=0.2s)
5.1.2 A=0.01m, increasing time periods (Ti=3.5s,Tf=3.8s, ΔT=0.1s)
5.1.3 A=0.01m, time period of 4s.
5.1.4 A=0.02m, decreasing time periods (Ti=4s,Tf=0.6s, ΔT=-0.2s)
5.1.5 A=0.04m, decreasing time periods (Ti=3s,Tf=1s, ΔT=-0.2s)
5.2 Irregular waves
PM spectrum, increasing peak periods Tp=1.05, 1.15, 1.27, 1.39, 1.49, 1.6, 1.7 and 1.75s.
Table 2.1 Test plan.
The collected data was delivered to the visiting team during the testing period. It includes one test log
excel file and three data files collected in each test (wave probe text file and two motion camera tsv files
containing 3D and 6D data).
2.3 Results
The presented preliminary results are just for model configuration 1. The full data analysis and results are
planned to be presented in international conferences and journals (see section 4.1).
2.3.1 Free Decay Tests
The heave and pitch time series for a couple of free decay tests are presented in Figures 12 and 13. First
estimates of heave and pitch’s eigenperiods read 3.5 and 6.2 seconds, respectively – which correspond to
18.2 and 32.0 seconds in real scale. Damping ratios were evaluated as 8 % (heave) and 5.61% (pitch).
Figure 12 – Heave’s free decay time series.
19
Figure 13 – Pitch’s free decay time series.
2.3.2 Stability Analysis
The inclining tests performed in the basin indicate to an intact GM of 5.4 cm. The numerically evaluated
one instead gives 3.2 cm, in which internal free-surface effects were taken into account for its evaluation.
Thus, an estimate of metacentric height for the full scale platform would lie between 0.8-1.5 meters.
The CG position as evaluated by the software is located 42.0 cm below the waterline. It differs in less than
1.0 cm, or 2.0%, from the previously estimated one. Centre of buoyancy in its turn is located 27.9 cm
below waterline.
The model pitch’s righting ARM (GZ) was numerically evaluated and is presented in Figure 14. The
downflooding angle is 90º. In order to assess the actual stability performance of the platform, it is still
necessary to account for wind drag and thrust force on the turbine. This is not done by now because
potential locations for the operation of the platform still need to be assessed.
Figure 14 – Pitch’s righting ARM (GZ) as a function of trim angle.
2.3.3 Hydrodynamic Analysis
The model motion RAOs for the modes of heave and pitch are presented in Figures 15 and 16, respectively.
All curves were evaluated considering head waves (180º incidence) as happened during the test.
In what concerns the hydrodynamic coefficients and the proprieties of the models, the simulations showed
that potential damping was far from reaching the measured damping ratio. This is related to the format
of the elements that cross the free-surface and the various small elements underwater. Non-linear viscous
damping thus plays a major role on the dynamics of the platform. The influence of non-linearity may also
be seen in Figures 15 and 16. As expected, the amplitude of response does not increase linearly with the
amplitude of the incoming wave, it actually follows a weaker trend. For instance, heave’s peak of response
drops almost by 50% from 1.0 cm to 2.0 cm wave amplitude.
20
Figure 15 – Heave RAOS.
Figure 16 – Pitch RAOS.
The response spectra on the same tested modes for the irregular waves’ scenarios are presented in Figures
17 and 18. Clearly, most of the energy of motion is located next to the natural frequencies, even though
seas’ most energetic bands are located somewhat far from these frequencies. The minor peaks on Figures
17 and 18 correspond exactly to these bands. Table 2 also show that with increasing wave energy, the
energy of response does not follow the theoretical trend. Indeed, the platform moves way less than linear
first order seakeeping theory predicts.
21
Figure 17 – Heave response spectra.
Figure 18 – Pitch response spectra.
On the other hand, the added mass on heave is about 30% of platform’s displacement; and on pitch is
59% of pitch’s inertia. Added mass on surge and sway are very much similar to platform’s displacement.
An extra run with no heave plates showed that almost all added mass on heave comes from the heave
plates’ dynamic effects.
Radius of gyration as evaluated from the full numerical model read 70.5 cm in pitch and 28.8 cm in yaw.
These values correspond to 36% of platform’s draft (for pitch) and 66% of the distance between central
and lateral columns’ centerlines. These values may be used as first estimates of radius of gyration in future
works.
22
Table 2.2 Significant Amplitude of Response
Sea State
Measure Heave [cm]
Theoretical Heave [cm]
Measured Pitch [cm]
Theoretical Pitch [cm]
1 0.959 2.832 1.349 1.770
2 3.862 3.885 2.059 3.149
3 3.749 5.029 1.824 4.551
4 4.068 6.494 2.365 5.837
5 4.197 8.345 1.950 6.984
6 8.267 10.39 2.096 8.045
7 9.817 13.24 2.391 8.920
2.4 Conclusions
The hybrid platform concept was analysed numerically and experimentally. The seakeeping and stability
performances of its hull were assessed and the results are promising. The characteristics regarding the
mass model, as well as the hydrodynamic characteristics of the hull are to be used in future studies as
first estimates for this kind of system/geometry.
The concept allows easy connection between its hull and 12 WECs around it, so the next step is to evaluate,
numerically and experimentally, the system working with all devices on. This brings numerical issues due
to the several degrees of freedom the whole assembled system possesses and due to the strong non-
linear effects acting on the small floaters. After all, as discussed in this report, non-linear effects already
play important roles on the main hull’s dynamics.
23
3 Main Learning Outcomes
3.1 Progress made
3.1.1 For This User-Group or Technology
The research plan was dedicated to the concept validation stage concerning the hydrodynamic damping
effects on the structure. The next research step is dedicated to the study of aerodynamic effects on the
structure by simulating the wind thrust forces on the wind turbine. So, the test plan (Table 2.1) will be
adapted in order to simulate the four model configurations for different wind conditions. Thus, the next
research activities will remain in the same development stage 1.
Meanwhile, the model will be upgraded with more PTO rotational dampers in order to simulate full PTO
damping, or in other words, damping of upward and downward WEC arm oscillations. These rotational
dampers operate in only one direction and offer no resistance in the opposite one, and so, each arm must
have two of these. However, it was not possible to acquire more than 12 dampers in time for the tests,
because the delivery time would be too long (~2months). The PTOs will be also upgraded with metallic
springs in order to simulate a Spring-Damper system.
Some metallic parts of the model deck will be replaced by lighter ones while the deck structure will be
reinforced in order to increase its rigidity. The objective of this upgrade is to install a bigger and heavier
wind turbine (higher mast and weight on top) in the deck and support bigger PTO damping forces, due to
the assembly of more rotational dampers. The damping heave plates will be, as well, replaced with bigger
and stronger ones.
Everything was new to the visiting team before and during the visit to the research infrastructure. The
team have progressed from a stage of pure numerical and theoretical analysis into another completely
different, the experimental one. New skills and experience had to be acquired in a short time in order to
design, build and test the model. So, the progress made by the team was huge and it continues, because
the data analysis is given the team a second opportunity to articulate what was learned in new and formal
knowledge. The team members are also more confident about their work.
3.1.2 For Marine Renewable Energy Industry
This is just a preliminary research work in a bigger project with the objective of evaluating and presenting
a hybrid FOWT concept that may contribute for the construction of bigger power rate FWOTs without
involving the construction of new shipyards and high renting fees. So, this is the main advantage the
concept presents to the industry. Further data analysis will present more results as regards to the
implications of using WECs on the platform stability.
3.2 Key Lessons Learned
The lessons learned are also advices for researchers that have limited resources to build up a prototype
and carry it to the research infrastructure, because these activities are not supported by Marinet2.
The applicants should evaluate if they have enough human, skills, experience, facility and financial
resources at their hosting institution to build up the prototype. The prototype scale may be adapted
in order to fit in the budget, however this should be discussed with the infrastructure manager in order
to have feedback as regards to the limitations of the wave basin.
A research chronogram should be created with the following tasks (adapted to the present case study)
organized in five main groups: Planning and warm up (infrastructure access planning, organization of
research materials and hydrodynamic modelling), Design for manufacturing (model deck and
submerged structure, hydrodynamic analysis), Construction (building and testing of the model deck
24
and submerged structure), Tests and Dissemination (paper preparation and submission, post-access
report).
The logistical issues are so important as the prototype construction phase. The team should be
prepared to change the prototype design in face of limitations, such as available materials and parts,
equipment and tools, transportation, not to mention the budget. However, this should be made without
undermining the main research objectives the team want to study.
Pay special attention to prototype transportation, in particular if travelling for long distances, because
the prototype may arrive at the research facility already damaged, and some test days are spent in
repairing it, in the best case scenario. So, the prototype should be designed to be robust and easily
repaired. Thus, if possible it is advisable to carry some extra parts and materials.
The prototype construction should include materials, such as polyurethane and silicone, in order to
protect the prototype from water leakages.
The prototype setup phase may take more time than the planned one. It depends on the skills and
experience of the visiting team, prototype damage, leakages, etc. So, the team should be patient and
hard worker. However, this phase will pay off the effort during the testing phase and is gratifying, in
particular for beginners.
The facility research staff may help a lot, so pay attention to their advices.
4 Further Information
4.1 Scientific Publications
Hallak, T., Gaspar J., Kamarlouei, M., Calvário, M., Mendes, M., Thiebaut, F., Soares, C. (Submitted). Numerical and experimental analysis of a hybrid wind-wave offshore platform’s hull. 37th International Conference on Ocean, Offshore and Artic Engineering, OMAE2018, June 17-22, 2018, Madrid, Spain.
Gaspar J., Kamarlouei, Hallak, T., M., Calvário, M., Mendes, M., Thiebaut, F., Soares, C. (In preparation). Design of a hybrid FOWT concept. 3rd International Conference on Renewable Energies Offshore, RENEW2018, October 8 – 10, 2018, Lisbon, Portugal.
Kamarlouei, M., Gaspar J., Hallak, T., Calvário, M., Mendes, M., Thiebaut, F., Soares, C. (In preparation). Experimental evaluation of a hybrid FOWT concept. 3rd International Conference on Renewable Energies Offshore, RENEW2018, October 8 – 10, 2018, Lisbon, Portugal.
Hallak, T., Gaspar J., Kamarlouei, M., Calvário, M., Mendes, M., Thiebaut, F., Soares, C. (In preparation). Numerical modelling of a hybrid FOWT concept. 3rd International Conference on Renewable Energies Offshore, RENEW2018, October 8 – 10, 2018, Lisbon, Portugal.
Gaspar J., Kamarlouei, Hallak, T., M., Calvário, M., Mendes, M., Thiebaut, F., Soares, C. (Planned). [Detailed explanation of the hybrid FOWT concept and design]. Renewable Energy.
Kamarlouei, M., Gaspar J., Hallak, T., Calvário, M., Mendes, M., Thiebaut, F., Soares, C. (Planned). [Detailed explanation of the concept experimental evaluation]. Renewable Energy.
Hallak, T., Gaspar J., Kamarlouei, M., Calvário, M., Mendes, M., Thiebaut, F., Soares, C. (Planned). [Detailed explanation of the concept numerical model]. Renewable Energy.
4.2 Website & Social Media
Online Photographs Link here
Online Video Link here
25
5 References
[1] Karimirad, M. 2014. Offshore Energy Structures: for wind power, wave energy and hybrid marine
platforms. Springer International Publishing. doi: 10.1007/978-3-319-12175-8.
[2] Lefebvre, S., Collu, M. 2012. Preliminary design of a floating support structure for a 5 MW offshore
wind turbine. Ocean Engineering, 40, pp. 15-26.
[3] Xiaojing, S., Huang, D., Wu, G. 2012. The current state of offshore wind energy technology
development. Energy 41, pp. 298-312.
[4] Crozier, A. 2011. Design and Dynamic Modeling of the support Structure for a 10 MW Offshore Wind
Turbine. Trondheim: NTNU – Norwegian University of Science and Technology.
[5] George, J. 2014. WindFloat design for different turbine sizes. UL – University of Lisbon.
[6] Wiser, R., Yang, Z., Hand, M., Hohmeyer, O., Jensen, P.H., et al. 2011. Wind Energy. In IPCC Special
Report on Renewable Energy Sources and Climate Change Mitigation. Cambridge: Cambridge University
Press.
[7] Karimirad, M. 2014. Offshore Energy Structures: For Wind Power, Wave Energy and Hybrid Maritime
Platforms. Springer. [REMOVER DA LISTA]
[8] Borg, M., Collu, M., Brennan, F. 2013. Use of a Wave Energy Converter as a Motion Suppression Device
for Floating Wind Turbines. In Energy Procedia, 35, pp. 223-233.
[9] Borg, M., Utrera Ortigado, E., Collu, M., Brennan, F.P. 2013. Passive damping systems for floating
vertical axis wind turbines analysis. In: Proceedings of the 10th deep sea offshore wind R and D
conference. Trondheim, Norway, 24-25 January.
[10] Engström, J., Eriksson, M., Göteman, M., Isberg, J., Leijon, M. 2013. Performance of large arrays of
point absorbing direct-driven wave energy converters. Journal of Applied Physics, 114 (20).
[11] Balitsky, P., Bacelli, G., Ringwood, J. 2014. Control-influenced layout optimization of arrays of wave
energy converters. In Proceedings ASME 33rd International Conference on Offshore Mechanics and Artic
Engineering, San Francisco, CA, USA, 2014.
[12] Sinha, A., Karmakar, D., Guedes Soares, C. 2015. Numerical modelling of array of heaving point
absorbers. C. Guedes Soares (Ed.), Renewable Energies Offshore, Taylor and Francis Group. London, UK,
pp. 383-391.
[13] Sinha, A., Karmakar, D., Guedes Soares, C. 2016. Performance of optimally tuned arrays of heaving
point absorbers. Renewable Energy, 92, pp. 517-531.
[14] Sinha, A., Karmakar, D., Gaspar, J., Calvário, M., Guedes Soares, C. 2016. Time domain analysis of
circular array of heaving point absorbers. Guedes Soares, C. & Santos T.A. (Eds.) Maritime Technology
and Engineering III. London, UK: Taylor & Francis Group: pp. 1133-1140. doi: 10.1201/b21890-152.
[15] Gaspar J., Kamarlouei M., Calvário, M., C. Guedes Soares. 2017. Floating Offshore Wind Turbine
(FOWT) with Controllable Waterplane Area. 2017 INORE North American Symposium, May 19 – 22,
Portland, Oregon.
[16] Hallak, T. S., Gaspar, J. F., Kamarlouei, M., Calvário, M., Mendes, M., Thiebaut, F., Guedes Soares,
C. (Submitted). Numerical and Experimental Analysis of a Hybrid Wind-Wave Offshore Platform’s Hull.
26
6 Appendices
6.1 Stage Development Summary Table
The table following offers an overview of the test programmes recommended by IEA-OES for each
Technology Readiness Level. This is only offered as a guide and is in no way extensive of the full test
programme that should be committed to at each TRL.
NASA Technology Readiness Levels1
1 https://www.nasa.gov/directorates/heo/scan/engineering/technology/txt_accordion1.html
27
NASA TRL Definition Hardware Description Software Description Exit Criteria
TRL Definition Hardware Description Software Description Exit Criteria
1 Basic principles observed and reported.
Scientific knowledge generated underpinning hardware technology concepts/applications.
Scientific knowledge generated underpinning basic properties of software architecture and mathematical formulation.
Peer reviewed publication of research underlying the proposed concept/application.
2 Technology concept and/or application formulated.
Invention begins, practical application is identified but is speculative, no experimental proof or detailed analysis is available to support the conjecture.
Practical application is identified but is speculative, no experimental proof or detailed analysis is available to support the conjecture. Basic properties of algorithms, representations and concepts defined. Basic principles coded. Experiments performed with synthetic data.
Documented description of the application/concept that addresses feasibility and benefit.
3 Analytical and experimental critical function and/or characteristic proof of concept.
Analytical studies place the technology in an appropriate context and laboratory demonstrations, modelling and simulation validate analytical prediction.
Development of limited functionality to validate critical properties and predictions using non-integrated software components.
Documented analytical/experimental results validating predictions of key parameters.
4 Component and/or breadboard validation in laboratory environment.
A low fidelity system/component breadboard is built and operated to demonstrate basic functionality and critical test environments, and associated performance predictions are defined relative to the final operating environment.
Key, functionally critical, software components are integrated, and functionally validated, to establish interoperability and begin architecture development. Relevant Environments defined and performance in this environment predicted.
Documented test Performance demonstrating agreement with analytical predictions. Documented definition of relevant environment.
5 Component and/or breadboard validation in relevant environment.
A medium fidelity system/component brassboard is built and operated to demonstrate overall performance in a simulated operational environment with realistic support elements that demonstrates overall performance in critical areas. Performance predictions are made for subsequent development phases.
End-to-end software elements implemented and interfaced with existing systems/simulations conforming to target environment. End-to-end software system, tested in relevant environment, meeting predicted performance. Operational environment performance predicted. Prototype implementations developed.
Documented test performance demonstrating agreement with analytical predictions. Documented definition of scaling requirements.
6 System/sub-system model or prototype demonstration in an operational environment.
A high fidelity system/component prototype that adequately addresses all critical scaling issues is built and operated in a relevant environment to demonstrate operations under critical environmental conditions.
Prototype implementations of the software demonstrated on full-scale realistic problems. Partially integrate with existing hardware/software systems. Limited documentation available. Engineering feasibility fully demonstrated.
Documented test performance demonstrating agreement with analytical predictions.
7 System prototype demonstration in an operational environment.
A high fidelity engineering unit that adequately addresses all critical scaling issues is built and operated in a relevant environment to demonstrate performance in the actual operational environment and platform (ground, airborne, or space).
Prototype software exists having all key functionality available for demonstration and test. Well integrated with operational hardware/software systems demonstrating operational feasibility. Most software bugs removed. Limited documentation available.
Documented test Performance demonstrating agreement with analytical predictions.
8 Actual system completed and "flight qualified" through test and demonstration.
The final product in its final configuration is successfully demonstrated through test and analysis for its intended operational environment and platform (ground, airborne, or space).
All software has been thoroughly debugged and fully integrated with all operational hardware and software systems. All user documentation, training documentation, and maintenance documentation completed. All functionality successfully demonstrated in simulated operational scenarios. Verification and Validation (V&V) completed.
Documented test performance verifying analytical predictions.
9 Actual system flight proven through successful mission operations.
The final product is successfully operated in an actual mission.
All software has been thoroughly debugged and fully integrated with all operational hardware/software systems. All documentation has been completed. Sustaining software engineering support is in place. System has been successfully operated in the operational environment.
Documented mission operational results
28
Rue d’Arlon 63-65 | 1040 Brussels |Tel. +32 (0)2 400 1040 | E. [email protected] | www.ETIPOcean.eu